Our main objective is to study the sequence of events and specificity in the formation of nerve-muscle and intraneuronal synapses in low-density cell cultures of embryonic muscle, spinal cord and sensory ganglia, plated in various combinations. Simultaneous microelectrode (recording, stimulating and iontophoretic) and time-lapse cinematographic techniques will be correlated with autoradiographic and electronmicroscopic findings. Attempts to separate specific cell types by microdissection, velocity sedimentation and affinity columns in order to obtain "pure" cultures containing only one presynaptic and one postsynaptic cell type will be made. Long-term changes in synaptic efficacy and trophic interactions between synaptically connected cells will be examined. In nerve-muscle cultures, we will study the development of postsynaptic ACh sensitivity, the long-term regulation of receptor distribution and the role of receptors in synapse formation.